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Red Cell Folate Testing

Unwarranted and Overutilized in the Era of Folic Acid Supplementation


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Mayo RBC/Serum Folate Orders 1999-2009

Slide 13

November 2010

We further undertook a 10-year retrospective analysis of red blood cell and serum folate results to examine ordering patterns and evaluate the clinical utility of RBC folate in our patient population. Results were retrieved from all serum and RBC folate tests from the laboratory information system at Mayo ordered on inpatients and outpatients between 1999-2009. Data for patients who had simultaneous orders for serum and red cell folate were analyzed and chart reviews were conducted on those patients with normal serum folate but low RBC folate; these are the individuals who have the potential for misdiagnosis if screened with a serum folate alone. Abnormal values were defined two-fold: first by our current reference ranges (<268 ng/mL, indicating red cell folate deficient; <4.0 ng/mL, indicating serum folate deficiency) and by the NHANES/CDC criteria for folate deficiency, which are serum folate <3.0 ng/mL and RBC folate <140 ng/mL. A total of 152,166 serum and 15,708 RBC folate assays were performed over the decade. The prevalence of folate deficiency using only serum folate was 0.39% and 0.27% when using only RBC folate. There were 1082 patients in which serum and RBC folate were ordered concurrently, which is shown in the table. Looking at the abnormal subset defined by our traditional reference ranges (top table), you can see only 39 individuals had a normal serum folate but abnormal red cell folate. Twenty-eight of the 39 actually had a normal red cell folate based on the reference range utilized at the time this assay was performed and therefore would not have been flagged as low. Three patients were documented as nonfasting, leading to inaccurate serum folate results, 5 patients were on the borderline of low and could be accounted for based on the imprecision of the assay, and 3 were considered "difficult interpretations," where there was no explanation for the low red cell folate. Using more traditional cutoffs, we evaluated the same set of patients (seen in the bottom table). In this analysis, only 1 (0.09%) individual had both an abnormal serum and RBC folate using traditional definitions for deficiency. Only 4 individuals had a normal serum folate but abnormal RBC folate; one which was nonfasting and the same 3 difficult interpretations as noted above. The following summarizes those 4 chart reviews: 1) a 6 year old.male with known genetic folic acid transporter deficiency treated with Leucovorin; 2) 58 year old male with history of gout, hypertension, psoriasis, and hyperlipidemia with normal hemoglobin (Hb) and MCV; 3) 65 year old male with chronic diarrhea and suspected alcohol abuse; slight macrocytosis (MCV=100.3 fL) but normal Hb; 4) 51 year old male with multifactorial gait disorder and alcohol abuse. There was a previous history of vitamin B12 deficiency in this last individual, but B12 levels were normal at this time. The CBC was notable for macrocytosis (MCV=115.1 fL) without anemia. Folate supplementation was initiated only in the last patient.

RBC/Serum Folate Orders 1999-2009


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